The rhabdoid tumor is an exceedingly rare renal tumor that occurs predominantly in infants and young children. The tumor is highly aggressive and has a poor prognosis (Weeks et al, 1989, 1991). The histogenesis is unknown. Rhabdoid tumors have now been reported in all age groups and in sites other than the kidney (Parham et al, 1994; Fanburg-Smith et al, 1998; Ogino et al, 2000).

In tissue sections, the tumor is composed of a single population of cells that may vary in size and configuration from round or oval to spindly. The characteristic feature of these tumors is the presence of large, eosinophilic cytoplasmic inclusions that displace the nucleus of the cell to the periphery. On electron microscopy, the inclusions are composed of intermediate filaments. There is no evidence that the cytoplasmic inclusions represent an accumulation of myoglobin, but it is the appearance that gave the tumor its name. Similar cytoplasmic inclusions that stain with an antibody to myoglobin may be observed in cells of rhabdomyosarcoma. From time to time, similar cytoplasmic inclusions may be observed in other tumors, including undifferentiated large-cell lung cancer. To our knowledge, there is only one published description of the cytologic findings in FNA biopsies of rhabdoid renal tumors. In three patients, Akhtar (1991) observed large polygonal cells with abundant dense pink cytoplasm, large intracytoplasmic eosinophilic inclusions, and large nuclei with macronucleoli. “Koss’ Diagnostic Cytology and Its Histopathologic Bases, 5th Edition”